Development of a child's spine
Children are not just small adults; their bodies are still developing and those developmental changes make them more vulnerable than an adult. A child’s vertebrae are connected via cartilage rather than ossified bone.
Those connections are called synchondroses, and are slowly closing over time.
There are three major points of ossification, each with two synchondroses. According to a study published in the Association for the Advancement of Automotive Medicine , the first station to close is the C3, second is the axis and third is the atlas. The results of the study show:
> 50% probability that the primary closure of the C3 is complete at age two and the secondary at age three.
> 50% probability that the primary closure of the axis is complete at age five and the secondary at age six.
> 50% probability that the primary closure of the atlas is complete at age seven and the secondary at age eight.
(Yoganandan, N., Pintar, F. A., Lew, S. M., Rao, R. D., & Rangarajan, N. (2011). Quantitative Analyses of Pediatric Cervical Spine Ossification Patterns Using Computed Tomography. Annals of Advances in Automotive Medicine / Annual Scientific Conference, 55, 159–168.)
This image shows the cervical (top), thoracic (middle), and lumbar (bottom) vertebrae of a one year old (left, each photo) and six year old (right, each photo). Note the easily visible synchondroses in each.
These findings show that before age two, none of the cartilaginous spaces have completed ossification. Those pieces of cartilage have the ability to stretch up to two inches. Yet only a 1/4 inch stretch is enough to rupture the spinal column, resulting in paralysis or death.
(McCall, T., Fassett, D., & Brockmeyer, D. (2006). Pediatric Cervical Spine Trauma in Children: A Review. Neurosurgical Focus, 20(2), 1-8.)
Sweden has been pioneers of rear facing with Professor Bertil Aldman of Chalmers University in Sweden designing the first rear-facing car seat in 1963 to protect a child’s head, neck and spine. The recommendation in Sweden is to rear face at least up to the age four, as it is determined that young children are best protected in rearward facing child restraints. The statistics from Sweden has shown the effectiveness of this recommendation:
From 1999 to 2006 four children aged under 4 years and restrained in rear facing seats were killed in Sweden. The deaths were due to fire, drowning, or excessive intrusion and were unrelated to the type of car seat. During the same period six children aged under 4 years in forward facing booster seats were killed. Three of these crashes would have been potentially survivable if the children had been travelling in rear facing seats.
Swedish accident research, of all serious crashes reported to Volvo’s insurance company from 1976 to 1996, has shown that rearward facing children’s car seats reduce serious injuries by 96% compared to forward-facing seats reducing injury by 77%. Isaksson-Hellman I, Jakobsson L, Gustafsson C, Norin H. Trends and effects of child restraint systems based on Volvo’s Swedish accident database. (Report No SAE 973299.)
Benjamin Hoffman is a Professor of Pediatrics at Oregon Health & Science University School of Medicine in Portland and a child injury prevention specialist. He states that:
“Younger children tend to have relatively bigger heads, weaker necks and muscles in general and looser tendon and ligaments. Facing forward, the head and neck are thrown forward violently in a crash, and the same forces that can lead to whiplash in an adult can actually cause the spine of a young child to separate and injure the spinal cord.”
But the force of impact is distributed differently when a child faces the back, Hoffman explained.
“If the child is rear-facing, all of the force is spread over the entire back of the child, allowing it to be absorbed by the seat, and cradling the head and neck to prevent injuries to that most vulnerable part of our body,” he said. “Arms and legs are almost never injured when rear-facing, and because kids are naturally flexible and adaptable, we see in real practice that they can always find a comfortable position, even on long trips.”
Hoffman said three reasons tend to hold parents back when it comes to following the recommendations: they want to be sure their child is comfortable, they want to be able to see their child and milestones—such as a child feeding themselves—are usually thought of as positive.
“Car seat safety is the one place where the next step is actually not positive since kids lose protection in transitioning from rear-facing to forward-facing, from forward-facing to booster seats, and so on,” Hoffman said. “Children are not little adults, and their unique developmental needs require accommodations.”
American Academy of Pediatrics Committee on Injury, Violence, and Poison Prevention (2011) Policy Statement—Child Passenger Safety. http://pediatrics.aappublications.org/content/pediatrics/early/2011/03/21/peds.2011-0213.full.pdf
Anund, A., Falkmer, T., Forsman, A. et al (2003) Child safety in cars – Literature review. VTI Report 489A, Swedish National Road and Transport Research Institute (VTI), Linkoping.
Arbogast, K.B., Cornejo, R.A., Kallan, M.J., Winston, F.K. & Durbin, D.R. (2002) Injuries to children in forward facing child restraints. Annual Proceedings. Association for the Advancement of Automotive Medicine 2002;46:213-30.
Brolin, K., Stockman, I., Andersson, M. et al (2015) Safety of children in cars: A review of biomechanical aspects and human body models. IATSS Research , Volume 38, Issue 2 , March 2015, Pages 92-102
Gloyns, P. & Roberts, R. (2008) An accident study of the performance of restraints used by children aged three years and under. A study commissioned by the ANEC (European Consumer Voice in Standardisation)
Henary, B., Sherwood. C.P., Crandall. J.R., Kent. R.W., Vaca. F.E. & Arbogast, K.B. (2007) Car safety seats for children: rear facing for best protection. Injury Prevention;13:398-402.
McMurry TL, Arbogast KB, Sherwood CP, et al (2017) Rear-facing versus forward-facing child restraints: an updated assessment . Injury Prevention Published Online First: 25 November 2017. doi: 10.1136/injuryprev-2017-042512
Kallan, M.J. Durbin, D. R og Arbogast, K.B. (2008) Children in Child Safety Seats Seating Patterns and Corresponding Risk of Injury Among 0- to 3-Year-Old. Pediatrics; 121;e1342
Sherwood, C. P. & Crandall , J.R. (2007) Frontal sled tests comparing rear and forward facing child restraints with 1-3 year old dummies. Annual Proceedings. Association for the Advancement of Automotive Medicine, 51: 169–180.
Stalnaker R.L. (1993) Spinal cord injuries to children in real world accidents. (Report No SAE 933100.) I: Proceedings of Child Occupant Protection 2nd Symposium. Warrendale, PA: Society of Automotive Engineers, 173-83.
Turchi, R., Altenhof, W., Kapoor, T. & Howard, A. (2004) An investigation into the head and neck injury potential of three-year-old children in forward and rearward facing child safety seats, International Journal of Crashworthiness, 9:4, 419-431
Watson, E.A. & Monteiro, M.J. (2009) Advise use of rear facing child car seats for children under 4 years old. British Medical Journal;338:b1994
Zweitzer, RE, Rink, RD, Corey, T & Goldsmith, J (2002) Children in motor vehicle collisions: analysis of injury by restraint use and seat location. Journal of Forensic Sciences, 47(5): 1049–1053.